Hi,
you can try it
.aspx page write javascript function like
<script type="text/javascript">
function chkEmail() {
alert('here implement textchange functions');
}
<script>
in body textbox
<asp:textbox id="TextBox1" runat="server" onblur="return chkEmail();" xmlns:asp="#unknown">
when ever you textchange it can working fine
happy coding.........</script></script>